Britannica Nobel Prize: Hafnium: Detailed overview and data.
ChemGlobe: Hafnium: Electronic, thermal, and steric data along with an isotope table.
ChemicalElements.com: Hafnium: Basic information, atomic structure, and isotopes.
EnvironmentalChemistry.com: Hafnium: Atomic structure, chemical and physical properties, and table of nuclides.
Hafnium: Data tables and historic information.
It's Elemental: Hafnium: Basic physical and historical information.
LANL: Hafnium: History, properties, uses, and handling.
Lenntech: Hafnium: Physical data, chemical properties, health and environmental effects.
Visual Elements: Hafnium: General and physical information, source, uses, key isotopes, and ionisation energies.
WebElements: Hafnium: Extensive information on history, uses, occurrence, compounds, and properties.
Wikipedia: Hafnium: Properties of the element, including its history, applications, and characteristics.